1. Field of the Invention
The present invention relates to a display device including a combination of a parallax barrier and an image generation device for generating displaying images, the display device being capable of displaying different images towards a plurality of display directions, respectively.
2. Description of the Related Art
Display devices displaying different images towards a plurality of viewpoints have been proposed as 3D display devices in which an image generation device, such as a display panel, and a viewing angle control unit, such as a parallax barrier, are used in combination. With these 3D display devices, as illustrated in FIG. 6, a certain viewing angle is provided by parallax barriers 102 arranged outside image generation device 101. Thus, as illustrated in FIG. 7, if the display device is viewed from a certain viewing area in a space, only the image corresponding to each eye is visually perceived. Accordingly, if the viewer views the 3D display device from a position within the viewing area where the left eye and right eye can visibly perceive only each corresponding image, a 3D image is recognized by the viewer.
Also, the use of the display device being able to display different images towards a plurality of viewpoints by combining the image generation device and the viewing angle control unit is not limited to such 3D displays. For example, it is also applicable for use in displays that display different images towards a plurality of viewers (hereafter referred as multiple-screen image display). In other words, with 3D displays, as illustrated in FIG. 8A, the right-eye image and the left-eye image separated according to the viewing angle using parallax barrier 102 positioned away from the display screen, is viewed by the viewer's right-eye and left-eye respectively. On the other hand, with a dual image display, as illustrated in FIG. 8B, a first image and a second image separated according to the viewing angle using parallax barrier 102 positioned close to the display screen are viewed by different viewers respectively.
FIG. 9 is a schematic cross sectional view illustrating an example of a display device in which an image generation device and a viewing angle control unit are combined. The display device illustrated in this figure includes a display panel 110, a parallax barrier 120, a backlight 130, and polarizing plates 141 and 142. FIG. 9 illustrates a structure using a transmissive type liquid crystal display panel as a display panel 110.
The backlight 130, as illustrated in FIG. 9, includes a light source 131 and a reflector section 132 such that light is irradiated towards a display panel 110 by reflecting the light irradiated from a light source 131 with a reflector section 132.
The display panel 110 is an active-matrix type liquid crystal display panel, including a liquid crystal layer 113 sandwiched between two glass substrates 111 and 112 facing each other. Between the glass substrate 111 and 112, a sealing material is positioned to encapsulate the liquid crystal layer 113.
The pixels, as illustrated in FIG. 9, are arranged, with pixel column L for the left-side image display (image display towards the left side of the display device) and pixel column R for the right-side image display (image display towards the right side of the display device) arranged alternately and so as to extend parallel to the extending direction of the data signal lines (not illustrated).
Also, on the surfaces of the glass substrates 111 and 112, which face each other, an alignment film (not illustrated) is provided. The alignment film has been subjected to an alignment process in directions orthogonal to each other. Each alignment film has been rubbed in each direction parallel to the surfaces of the substrates. The polarizing plate 141 is provided on that side of the glass substrate 111, which faces the backlight 130. The polarizing plate 142 is provided on that side of the parallax barrier 120 which is opposite to the displaying side of the parallax barrier 120 (opposite to backlight 130).
The parallax barrier 120 includes a barrier glass 121 and a light-shielding layer 122. The light-shielding layer 122 is illuminated by the backlight 130, and by shielding a portion of the light passed through display panel 110, the light-shielding layer 122 is specific to the display images.
Also, the parallax barrier 120 and display panel 110 are bonded with a resin layer 151 with a certain space therebetween.
However, the conventional structure has a problem in that after the bonding of parallax barrier 120 and display panel 110, peeling of parallax barrier 120 readily occurs. The explanation of the problem is as follows.
Firstly, the parallax barrier 120 is required to be a smaller size than a bonding substrate of the display panel 110 (the glass substrate 112), so that the parallax barrier 120 can be bonded together with the display panel 110 without protruding from an outer edge of the display panel 110 (in order to prevent hooking and cracks).
In addition, with recent display devices, in order to downsize, as shown in FIG. 10, a circuit 160, such as a driving circuit for driving a display panel 110, may be formed on the circuit connection area on the surface of the glass substrate 111 composing display panel 110. In addition, with a display device using the parallax barrier 120, usually, the glass substrate 112 that is that one of the substrates which faces toward the parallax barrier 120 is extremely thin.
The thin thickness of the glass substrate 112 is to satisfy a demand to give a thin overall thickness to the display devices having the parallax barrier 120, which tend to have a thick thickness compared to display devices not having the parallax barrier 120.
Since the substrate 112 facing the parallax barrier 120 is bonded with the parallax barrier 120, the thin thickness of the glass substrate 112 itself will not lead to deformation of the liquid crystal layer 113. In addition, there is a trend in the recent technology development to improve the display devices to attain a thinner thickness of glass substrate (see Japan Unexamined Patent Application Publication, Tokukaihei, No. 4-116619 (published Apr. 17, 1992)).
Furthermore, with display devices that display a plurality of different images towards a plurality of viewers, it is required to make the distance between the parallax barrier and the image generation device extremely short (compared to a 3D display) (see Japan Unexamined Patent Application Publication, Tokukai, No. 2005-78094 (published on Mar. 24, 2005)). Therefore, with the display panel 110 using the parallax barrier 120, as shown in FIG. 10, there are display areas with thinner thicknesses than the thickness of the circuit connection area (the total thickness of the glass substrate 111 and the thickness of circuit 160). In this case, the parallax barrier 120 needs to have such a size that the parallax barrier 120 will not contact the circuit 160.
In addition, the barrier pattern in the parallax barrier 120 should be bigger than or around the same size (area) as the display area of the liquid crystal panel 110 (the area where image will be displayed by pixels). Therefore, with the conventional parallax barrier 120, the barrier pattern is fully formed on the parallax barrier 120.
However, in the conventional display device including the parallax barrier 120 and display panel 110 bonded together, as shown in FIG. 10, peeling of parallax barrier 120 at the edge portions of the bonding surface occur. The reasons for this can be surmised as follows.
Firstly, the strength is different between the parallax barrier 120 having only one substrate (the barrier glass 121) and the display panel 110 in which two glass substrates 111 and 112 are bonded together. Furthermore, the parallax barrier 120 and display panel 110 are bonded by using resin layer 151 including an ultraviolet curing resin, and the resin layer 151 is cured by being irradiated by ultraviolet rays from above the parallax barrier 120. At this time, there is a portion of the resin layer 151 where ultraviolet rays inadequately irradiate due to the light-shielding layer 122 in the parallax barrier 120, and in this portion of the resin layer 151 does not cure adequately and a lack of adhesion occurs.
After bonding the parallax barrier 120 and display panel 110, external influences such as heat cause strain due to the differences in coefficient of thermal shrinkage between materials. If this strain is great, peeling occurs in the weakest portion of the bonding surface, in other words the edge portions of the bonding portions.
For example, if the polarizing plate 142 bonded with the parallax barrier 120 shrinks, the barrier substrate 121 is pulled, thereby generating a warp at the edge portion of this barrier substrate 121. At this time, since the display panel 110 including two substrates bonded together has suitable strength, the display panel 110 is unlikely to be warped, but the adhesive layer 151 being the interface between the parallax barrier 120 and display panel 110 peels off.
Consequently, the inventors of the present application developed a display device including a parallax barrier and a display panel wherein the display device has an area where a light-shielding layer is not formed on the peripheral portions of the parallax barrier so that peeling on bonding surfaces of the parallax barrier and display panel will be unlikely to occur (this display device still has not been made public or published as of the filing of present application).
However, the inventors discovered that in a case where the positioning and arrangement of sealing material 114 is not adequate, for example, when sealing material 114 is positioned as shown in FIG. 11, display non-uniformity (light and shade) is generated around the edge area 120a on the parallax barrier 120 in the display device of this configuration. The reasons for this can be surmised as follows.
As explained previously, the parallax barrier 120 and the display panel 110 are bonded together using the resin layer 151 including an ultraviolet curing resin, and ultraviolet ray is irradiated from above the parallax barrier 120. In bonding the parallax barrier 120 and the display panel 110, the adhesion state therebetween are different between the area with the light-shielding layer 122 (parallax barrier) within the display area, and the area without a light-shielding layer 122 (parallax barrier) (edge area 120a) on the peripheral portions of the parallax barrier 120.
In the case where the glass substrate 112 being bonded to the parallax barrier 120 is thick, a difference in adhesion state does not become a problem. However, with the display device using the parallax barrier 120, as explained previously, the glass substrate 112 being bonded to the parallax barrier 120 is extremely thin. Therefore, the difference in the adhesion state puts a strain on the glass substrate 112, and this strain causes non-uniformity in thickness of the liquid crystal layer 113. This non-uniformity in thickness of the liquid crystal layer 113 will be seen by a viewer as non-uniform brightness of the displayed image.
It is deduced that the strain of the glass substrate 112 caused by the difference in adhesion state between the areas with light-shielding layer 122 and areas without light-shielding layer 122 is caused due to the following reasons.
Firstly, in the resin layer 151, there is a difference in coefficient of curing shrinkage between the area with the light-shielding layer 122 and the area without the light-shielding layer 122, since the amount of ultraviolet radiation differs between the area with the light-shielding layer 122 and the area without the light-shielding layer 122. Specifically, the amount of ultraviolet radiation towards the resin layer 151 for areas without the light-shielding layer 122 is greater than the amount of ultraviolet radiation towards an area with the light-shielding layer 122. Therefore, the coefficient of curing shrinkage of the resin layer 151 at the edge portion of the parallax barrier 120 (the portion without the light-shielding layer 122) is greater than the resin layer 151 within the portion with the light-shielding layer 122 in the parallax barrier 120. Thus, it is considered that at the edge portion of the parallax barrier 120 with the greater coefficient of curing shrinkage in the resin 151, the thin glass substrate 112 is restrained from being pulled towards the display panel 110.
In addition, since the amount of ultraviolet radiation towards the resin layer 151 in the area without the light-shielding layer 122 is greater than the amount of ultraviolet radiation towards the resin layer 151 in the area with the light-shielding 122, the adhesion force of the resin layer 151 in the edge portion of the parallax barrier 120 (the portion without the light-shielding 122) is strong. Therefore, it is considered that the glass substrate 112 strained from the stress caused by the thermal shrinkage of members such as the barrier glass 121 and the glass substrate 112 being concentrated towards the edge portions of the parallax barrier 120 having strong adhesion force.
Especially, the problem is significant with multiple-image display devices using thin substrates. With multiple-image display devices, it is required to shorten the distance between the parallax barrier and the image generation surface of the image generation device, and as a substrate on the parallax barrier side of the image generation device, usually a substrate with a thickness of 30 μm to 170 μm, preferably 40 μm to 100 μm is used. For example, if providing rightward and leftward viewing angles to display different images to viewers, it is required to set the distance between the parallax barrier and the image generation surface of the image generation device (for example, the thickness of “adhesive layer 151 and glass substrate 112” in FIG. 9) to 60 μm to 200 μm. This distance is decided considering the thickness of this adhesive layer.